As the inner liner of a pneumatic tire, a rubber layer containing a butyl rubber with a low gas permeability (high gas barrier property) as the main component is generally used. In response to the recent requirement for saving the weight of a tire, the use of a thermoplastic resin film exhibiting a lower gas permeability is proposed.
For example, Patent Document 1 describes an inner liner formed by laminating a non-vent layer formed of an ethylene-vinyl alcohol copolymer film (hereinafter sometimes referred to as “EVOH”) or a polyvinylidene chloride film, both of which have an extremely low gas permeability, and an adhesive layer formed of polyethylene, polypropylene, or the like.
However, an inner liner formed of the thermoplastic resin film has little flexibility so that it cannot follow the expansion and contraction of the material while the tire runs. This may cause cracks. To solve this problem, various technologies are proposed.
For example, Patent Document 2 proposes that a thermoplastic resin film formed of a modified EVOH obtained by reacting an epoxy compound with EVOH is used for an inner liner to decrease the modulus of EVOH so as to prevent fractions and cracks when the inner liner is bent. Patent Document 3 proposes that the bonded surface of an inner liner formed of a thermoplastic resin film, which is bonded to the carcass, be subjected to surface oxidation to improve the peel strength and fracture resistance when the inner liner is bent so as to reduce the generation of cracks.